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“If sandscaping works we can implement it immediately.”

Posted at 08/08/2023 by Evelien van Eijsbergen

How do we stop the erosion of the river bed? And what measures can help? These are important tasks within the Integral River Management Program in the coming years. Kees Sloff (Deltares, TU Delft) is supervising the upcoming PhD student during the research and is very confident about one of the possible measures: adding sediment to the groynes. The first measurements are a fact and soon the first suppletions will start. Curious about the process and the first insights? Kees tells you all about it.

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Evelien van Eijsbergen


The reason

The bottom of the Waal River is slowly eroding, partly due to human activity. Within the Integrated River Management Program, it has been established that measures must be taken to reduce river bottom erosion. One of these measures is sediment replenishment; the starting point of this study. Kees explains, “Adding sediment in the middle of the river can cause problems for shipping. Then we thought: what about if you do this on the side of the river and let it flow back slowly?”

Promising measure

Adding sediment in the groynes seems a promising measure, but there are also many questions. How will the sediment later be returned from the groynes into the rivers, and how fast will it do so? Kees talks about the “sand motor,” an important term within this research. “By placing the sediment on the sides of the river it is not in the way of shipping. But because of the ships passing by, the sediment slowly comes from the groynes into the river. This is a “sand motor”: the lack of sand is slowly replenished, stopping the river bottom from eroding. Completely in line with the building with nature philosophy.”

“We first measure extensively what happens to the currents and waves in the groynes and around the replenishment due to shipping. The sand is applied just below the water level for the measurements,” Kees mentions. These are complex currents, so the researcher has to work with complex calculation models. After the measurements, it is therefore a matter of optimizing the models. “At some point, the model is good enough to reproduce simplified reality. This is very important for scaling up so that it can be applicable to many rivers.”

Of great importance

Kees sees both societal and scientific relevance for this research. “We contribute directly to the policy task of stopping soil erosion. Also, the complex connection between shipping and the impact on rivers is currently still a great unknown. We hope to change that.” According to Kees, this is not the only knowledge gain. “The ‘sand motor’ is designed in such a way that we hope it will also have added value for nature. For example, what effect does it have on fish? This in turn we can share with biologists: literally bycatch!”

The first insights

A baseline measurement was taken, the first measurements are a fact, and the replenishment will soon take place at three locations in the Waal. Kees talks about the first measurements: “Then you just stand in the water with your bare feet and feel in the groyne area how fast the current is and how this changes when a ship passes by. This of course doesn’t allow you to feel how fast it flows, but it’s fantastic to experience. For exact numbers, we do the measurements. We’ve already collected a lot of this kind of data and much of it we understand very well now.”

Collaboration with Rivers2Morrow

“For me, Rivers2Morrow is really a link between Rijkswaterstaat and knowledge development.” According to Kees, the research therefore fits well within the program. “If this project works and we have the knowledge in place, it can actually be implemented immediately. I am really hopeful, partly because of the enthusiasm from Rijkswaterstaat. We notice this for example by the cooperation in the measurements.” At the moment, the recruitment of the PhD student is in full swing. Kees notices that Rivers2Morrow is very important to the PhD students: “They are really part of a whole. We have also seen this with previous students. It is really focused on the rivers, making it a nice and small community.”
Wondering what the measurements looked like? Check out this video:

Last modified: 26/09/2023